Hacking into the electronics of Wii controllers seems to be a very popular thing to do. Ryan Culy made this very nice adaptation for a disabled friend:

"This custom Wii nunchuk was something that I designed for a good friend. His left arm only extends a little below the elbow, yet he has always been able to use videogame controllers with little difficulty.Unfortunately, most games for the Wii require the use of the nunchuk attachment, and holding two separate pieces for motion controls was not an option for him. Although my redesign for the nunchuk is intended to be used at the elbow with the joystick resting on a knee, it is simple enough that it could be used on a foot as well. The two buttons from the nunchuk were moved to the side of the Wii-remote where they can be easily pressed with the middle and index fingers".

More fantastic Wii Hacks at Johny Chung Lee - including the possibility of head-tracker control over Wii games.